They are all there, under the bed, in the closet, lurking in that haunted house . . . The things that go bump in the night exist, lurking in the dark, awaiting their chance to reach out with a clawed hand and snatch the unsuspecting. Their variety is that of the lore of the world and yet only the very young or the magically aware ever bother to perceive them. Many come to the bidding of a spell, others seem to leak out of the NeverNever into the mortal world while still more are 'created' there through some sequence of events. Always, they have to be stopped and thus the need for the Wardens.
Demon: called to the mortal world.